Spironolactone is being clinically evaluated for efficacy and safety in the treatment of acne vulgaris in adolescents and young adults. We have been able to develop a new quantitation procedure for spironolactone and its predominant metabolite.. canrenone from biological fluids that can provide a sensitivity of 1-2 ng/ml for both compounds. We are in the process of accumulating some data on assay validation. The protocol asks for topical application of 1 ml of a 2.5% solution of the drug in an alcohol based carrier vehicle to be applied topically 3 times a day which will probably result in low level of both drug and metabolite. We have found it necessary to develop a sensitive and specific assay which measures both the parent compound and its active metabolite. Overall variability in assay appears to be less than 7%.